A High-Speed Soft Startup Method With Full-Load Startup Capability for CLLC Converters

The CLLC converter is a high-frequency, high-efficiency isolated bidirectional DC/DC converter. For application scenarios like data center and battery energy storage (BES) systems, a high-speed soft startup with load is important for improving system dynamic response ability. In this paper, an optimized variable duty cycle soft startup method with full-load startup capability is proposed for CLLC converters. Specifically, an optimal duty cycle variation law is derived accurately to maintain the maximum resonant current in the whole startup process. Firstly, a special operation condition with energy limitation features is introduced ahead, where the core idea of the proposed method is emphasized. After that, the operation mode analysis method is used to analyze the detail working principle for different duty cycle, and the relationship among resonant current, duty cycle and output voltage is illustrated. Secondly, detail application framework of proposed method is given, and corresponding duty cycle optimization process is introduced carefully. Moreover, an accurate mathematical model of the load starting capability of the proposed method is established, which proves that the proposed method can realize a full-load startup. Finally, a 900W lab-level CLLC prototype is built for experiment verification: the accuracy of the theoretical mode analysis is verified firstly, then a high-speed no-load startup is realized in 9ms for the proposed method, which is nearly 9 times faster than the conventional varying frequency method, and a full-load startup is also achieved successfully in 14ms.